That's because the values are in different events as you can see in the table.
Are there only these three events always? If not , is there an identifier which could co-relate these events?
For the existing data example, try below
| eval PowerTime=if((AlarmID="25622"),Occurtime,null)
| eval NodeBTime=if((AlarmID="22214"),Occurtime,null)
| eval CellTime=if((AlarmID="29245"),Occurtime,null)
| eventstats values(PowerTime) as PowerTime,values(NodeBTime) as NodeBTime,values(CellTime) as CellTime
| " rest of your substraction calculations"
If you have multiple events and an common identifier to co-relate the events, you can add by that_identifier in the eventstats